Deformable bi-stable devices are known in the art, and have found many practical applications. Deformable bi-stable devices have been used in a variety of mechanical and electromechanical applications that require a deformable component to occupy one of two stable positions, while being unstable at positions intermediate to the two stable positions. In one application, a deformable bi-stable device may be used as a user input device such as a push-button as commonly used in many devices, including but not limited to computers, telephones, and vehicle control panels. A bi-stable device may be used as a push-button input for such applications where the button will occupy either an “in” or depressed position, or an “out” or undepressed position.
One example of a simple deformable bi-stable device that may be used for such applications is shown in FIGS. 1A and 1B. FIGS. 1A and 1B depict a schematic diagram of an exemplary reconfigurable bi-stable device 10 having a circular deformable panel 14. In FIGS. 1A and 1B, a cylindrical mounting member 12 having an upper lip portion 13 is mounted on a support structure 11. An elastically deformable circular panel 14 is attached to the inner circumference of the mounting member. The elastically deformable panel would have a normally flat state, but is sized to have a diameter in its normal flat state that is greater than the internal diameter of the mounting member 12 so that when it is mounted in the mounting member it is placed under a force load along vectors between opposing points on the circumference of the panel (in the horizontal plane as shown in FIG. 1). This load causes the elastically deformable panel to deform into one of two stable states, described for sake of convenience as an upper or first stable position depicted in FIG. 1A and a lower or second stable position depicted in FIG. 1B. The panel thus acts as a bi-stable snap-action panel, deformable between a convex (from the perspective above) stable configuration and a concave (from the perspective above) stable configuration. This configuration is also sometimes referred to as the “oil-can” configuration because the bi-stable snap action deformation was used in traditional old-style oil cans to displace oil out of an opening in the can. Lip portion 13 of the mounting member provides a convenient location to which to connect any additional components and also serves to conceal any such components and also the mounting location of the panel to the mounting member.
Another well-known deformable bi-stable device is known as the cylindrical shell configuration. This configuration is sometimes also referred to as the “tape measure” or “carpenter's tape” configuration because it is commonly seen in roll-up carpenter tape measures. An exemplary embodiment configuration is shown in FIGS. 2A and 2B. In FIG. 2A, the deformable bi-stable device 20 is shown in a first stable longitudinally straight configuration having a curvature that runs transverse to the longitudinal direction of the straightened structure. The transverse curvature is exaggerated in FIG. 2A for purposes of illustration, and the curvature is often much less severe in most tape measure configurations. In FIG. 2B, the deformable bi-stable device 20 is shown in a second stable coiled configuration. The device 20 may also have other stable kinked configurations, provided that care is taken not to kink the structure beyond the limits of elastic deformation.
The phenomenon of bi-stability may be graphically represented by a plot of potential energy of the deformable member versus its position or degree of deformation. Such plots are depicted in FIGS. 3A and 3B, which represent a plot of potential energy, E, of the deformable member of the bi-stable device on the Y axis, versus the position, P, or degree of displacement of the deformable member on the X axis. In both FIGS. 3A and 3B, positions P1 and P3 represent stable positions (e.g., the upper stable position of deformable member 14 in FIG. 1A and the lower stable position of deformable member 14 in FIG. 1B). Positions P1 and P3 on the plots of FIGS. 3A and 3B are also known as “energy wells”. All of the positions along the plots between P1 and P3 represent unstable transitory positions that the deformable member passes through while moving from position P1 to position P3. Position P2 is a position of maximum instability, which would be represented by the deformable member 14 in FIG. 1 being in a position halfway between that shown in FIGS. 1A and 1B.
Compared to the plot shown in FIG. 3A, the plot shown in FIG. 3B has relatively shallow energy wells. A device with such characteristics would be relatively easy to move between stable positions. However, those positions may not be sufficiently stable for many applications, such that vibration, jolts, or incidental external contact could cause the FIG. 3B device to undesirably move from one of the stable positions to the other stable position. The plot shown in FIG. 3A, on the other hand, represents a device with fairly deep energy wells. A device with such characteristics would be more highly resistant to unintended and undesired movement between stable positions. However, the steepness of the energy wells and the relatively greater energy levels required to move from one of the stable positions up to the peak at P2 in order to get to the other stable position may make the FIG. 3A device too difficult to move between stable positions, rendering it unsuitable for many applications. Thus, there continues to be a need for deformable bi-stable devices that offer good stability of the stable positions, but that can be readily moved between the stable positions when desired.